Multicomponent fibers and methods of fibrillating multicomponent fibers to create fine fibers are known in the art. Multicomponent fibers, also referred to as "conjugate fibers" or "fibrillatable fibers", contain at least two components that occupy distinct cross-sections along substantially the entire length of the fiber. They are typically produced by simultaneously and continuously extruding a plurality of molten fiber forming polymers through spinning orifices of a spinneret to form unitary filament strands. The composition of the individual components, which collectively comprise the multicomponent fibers, are often selected from dissimilar polymers which are not miscible in one another and which further have different coefficients of contraction, different solubility characteristics and/or other distinct physical properties. In this regard the selection of the polymers for the individual components or segments is often limited by the properties required for separation of adjacent segments.
One method which has been used to fibrillate unitary multicomponent fibers is to cause disparative swelling and shrinkage of one of the components relative to the others. This causes separation of the multicomponent fibers into two or more of its individual components. For example, U.S. Pat. No. 3,966,865 issued to Nishida et al. discloses a method of forming synthetic fibrous structures from multicomponent fibers in which the individual components may comprise a polyamide and either a polyester, polyolefin or polyacrylonitrile. The polyamide component is swelled and shrunk by treatment with an aqueous solution of an alcohol, such as benzyl alcohol or phenylethyl alcohol, causing separation. Similarly, U.S. Pat. No. 4,369,156 issued to Mathes et al. discloses a process for separating a multicomponent fiber of a copolyamide and a polyester by treatment with liquid or vaporous water 10-20.degree. C. below the softening point of the copolyamide. This treatment causes disparative shrinkage of the polymers and, thus, separation. However, separation by such processes may result in low and/or uneven fibrillation as well as fibers or fabrics which have lost desired characteristics, e.g. softness and bulk. In addition, such processes often require complex and lengthy processing which may also generate by-products which are costly to dispose.
Another method employed in separating the individual components of a multicomponent fiber is coextruding incompatible fiber-forming polymers into a unitary fiber and then dissolving one of the polymers thereby freeing the insoluble components. For example, U.S. Pat. No. 5,405,698 to Dugan teaches a multicomponent fiber composed of a plurality of water-insoluble polyolefin filaments surrounded by a water-soluble polymer. Such a configuration is often referred to as an "islands-in-sea" type fiber. The multicomponent fiber is treated with water thereby dissolving the water-soluble polymer and releasing the individual water-insoluble polyolefin filaments. Similarly, U.S. Pat. No. 4,460,649 issued to Park et al. teaches a multicomponent fiber composed of a polyamide and a polyester having wedged shaped segments surrounded by an outer component which is part of a central core. The outer component may be removed by a chemical process, such as treatment with an acid or alkali, and the remaining components separated by a swelling agent. However, separation in accord with such processes often utilizes polymers and/or solvents which are uneconomical and which generate considerable by-products which are environmentally undesirable and costly to dispose. Furthermore, such processes may result in fibers which have lost desired characteristics, i.e. softness, due to the chemical treatments. It is also important to note that such process inherently cause a considerable loss in bulk due to the removal of a substantial portion of the polymeric material forming the initial multicomponent fibers.
Thus, there exists a need for a method of producing a nonwoven web from splittable multicomponent fibers and a method for fibrillating the multicomponent fibers which does not destroy or degrade the desired characteristics of the polymeric fibers and/or the web resulting therefrom. There further exists a need for such a process which allows a wider variety of compatible polymers for use in splittable multicomponent fibers. Additionally, there exists a need for nonwoven webs and articles made therefrom having durable microfibers, a soft cloth-like feel, good bulk, high coverage (opacity), good barrier properties and improved hydroentangling processing characteristics.